Relevant Water Quality Parameters Research Articles

PocketWATCH: design and operation of a multi-use test bed for water Cherenkov detector components in pure and gadolinium loaded water

The PocketWATCH facility is a unique multi-purpose test bed designed to replicate the conditions of large water Cherenkov detectors. Housed at the University of Sheffield, the facility consists of a light-tight 2000 L ultrapure water tank with purification and temperature control systems. Water temperature, resistivity, and UV attenuation in the tank are monitored and shown to be stable over time. The system is also shown to be compatible with a solution of 0.2% gadolinium sulfate, allowing further utility in testing equipment bound for the next generation neutrino and nucleon decay water Cherenkov particle detectors. The relevant water quality parameters are shown to be stable whilst running in Gd-mode, thereby providing a suitable test bed for hardware development in a realistic, ex situ environment.

Evaluating protein skimmer performance in a commercial seawater recirculating aquaculture system (RAS)

Combining protein skimming with ozone (O3) is a common method for removing microparticles in recirculating aquaculture systems (RAS). Nevertheless, there is a limited number of studies that have validated protein skimming's performance at a commercial scale. Additionally, variations in protein skimmer designs and operational variables may yield different performance outcomes. In the present study, the performance of two types of full-scale protein skimmer (S1 and S2) were compared and evaluated under two levels of hydraulic retention time (HRT) (1.8 and 2.2 min) and three levels of O3 doses (0, 7, and 14 g O3/kg feed) in a commercial seawater RAS facility. Samples from the inlet and outlet of the protein skimmers were collected at each combination of operational variables. They were analysed for several relevant water quality parameters to quantify the treatment efficiency. O3 dose significantly improved water quality and reduced the numbers of microparticles and bacterial activity in a single pass. Besides that, doses as high as 14 g O3/kg feed significantly increased total residual oxidant (TRO) concentration. Additionally, an increase in HRT exerted a moderate effect on removing microparticles and a strong effect on redox potential (ORP) and TRO. Finally, the type of protein skimmer only affected the ORP, causing no significant changes to other water quality metrics. The correlations between the investigated water quality parameters defined a clear pattern of the ongoing processes and particle characteristics. Overall, the results demonstrated that protein skimming combined with carefully selected O3 doses can improve general water quality and control critical factors such as bacterial activity and microparticles under commercial operations.

Groundwater quality assessment using the WQI and GIS mapping: Suitability for drinking and irrigation usage in the Sirdala block of Nawada district

Abstract In the present study, the suitability of groundwater for drinking and irrigation purpose were analyzed. A total of 65 groundwater samples were collected and analyzed for relevant water quality parameters from Sirdala block of Nawada district Bihar (India). To estimate the WQI for the drinking purpose, various parameters such as pH, TDS, TH, AS and major ions (Ca2+, Mg2+, Na+, K+, Cl−, F−, HCO3−, NO3−, SO42−) were considered. The WQI for irrigation, various irrigation indices namely soluble sodium percent (Na%), sodium adsorption ratio (SAR), residual sodium bicarbonate (RSCB), permeability index (PI), magnesium hazards ratio (MHR), Kelly's ratio (KR), potential salinity (PS), Cl−: HCO3−, Mg(2+): Ca(2+) and Na+: Ca(2+) were employed and discussed in addition with Wilcox and USSL diagram. Plots, namely Gibbs ratio and Piper diagram, were used to understand chemical characteristics of groundwater. The WQI for drinking purpose was observed between 57.67 and 929.90 in which most samples (70.76%) were unsuitable for drinking. However, the WQI for irrigation purpose varied from 87.88 to 434.67 in which 50% of samples were suitable. Gibb's plots determined in this study reveal that evaporation-precipitation was the dominant factor that influences hydrochemistry. Piper plots suggest that Na-HCO3− water type was major hydrochemical facies in groundwater.

Accumulation of Heavy Metals by Some Aquatic Macrophytes in Two Streams along the Tiko-Douala Highway, Cameroon

Aims: This study was aimed at determining the ecological health of two roadside streams across the Tiko-Douala highway, Cameroon, and investigating the phytoremediation potentials of dominant aquatic macrophytes within these streams.
 Study Design: Water, sediments, and aquatic plant samples were collected from Camp 7 and Moqouo streams, and analyzed for ammonium nitrogen, nitrate nitrogen, phosphates, magnesium, cadmium, and lead, including other relevant water quality parameters.
 Place and Duration of Study: In the Life Science Laboratory of the University of Buea, and Soil and Water Laboratory of the University of Dschang, Cameroon between June 2021 and June 2022.
 Methodology: Six water samples and six sediment samples were collected per stream, and two of the most dominant plant species (Pennisetum purpureum Schumach (Poaceae) and Dicanthelium clandestinum L. (Poaceae) from Camp 7, Commelina benghalensis L. (Commelinaceae) and Oldenlandia corymbosa L.(Rubiaceae) from Moqouo stream) were collected for heavy metal analysis. Heavy metal concentration and bioaccumulation factors were determined for each plant.
 
 Results: High concentrations of phosphates were recorded in Camp 7 (1.19 mg/L) and Moqouo (2.17 mg/L) streams. Dissolved oxygen levels were 0.69 mg/L and 0.80 mg/L in Camp 7 and Moqouo respectively. Sediment cadmium levels ranged from 0.33± 0.02 to 0.63± 0.16 mg/kg, and lead ranged from 0.34 ±0.03 to 0.37 ± 0.12 mg/kg in Moqouo and Camp 7 respectively. 
 Conclusion: The Mouqouo and Camp 7 streams are rich in phosphates and thus not suitable for drinking and irrigation. Cadmium and lead in stream water were within the permissible limits but sediments contained higher concentrations than water and therefore they could be released gradually into the water column. All plants in the study except (Dicanthelium cladestinum) accumulated cadmium and lead, and could be potential plants for the phytoremediation of these metals.

Arsenic in groundwater from Southwest Bangladesh: Sources, water quality, and potential health concern

Arsenic (As) poisoning in groundwater has become one of the greatest environmental concerns around the world. In this study, As concentration in the groundwater samples (depth: 52–70 m) of southwestern Bangladesh was evaluated using Atomic Absorption Spectrometer (AAS) to know the current status, possible source(s), and probable health risk of As. In addition, the other relevant water quality parameters (pH, temperature, EC, TDS, Na+, K+, Ca2+, Mg2+, Cl−, NO3−, SO42−, HCO3−, Fe, and Mn) were also measured using various instruments such as portable bench meter, Flame photometer, AAS, and Ion Chromatograph to evaluate the suitability of the water for drinking and irrigation purposes. Arsenic concentration (μg L−1) ranged from 13.10 to 292 (mean ± SD: 156.9 ± 100.31), which is alarmingly, and 15 times higher than the WHO recommended value for drinking water. pH values of collected groundwater samples ranged from 7.17 to 8.09, which exhibits a lightly alkaline nature. The average abundance of major cation follows the order of Ca2+ > Mg2+ > Na+ > K+, and the average abundance of major anions follows the order of HCO3− > Cl− > NO3− > SO42−, with Ca2+and HCO3− being the dominant cation and anion, respectively. Based on water quality assessments utilizing the water quality index and entropy water quality index, the groundwater in the region of interest was not suitable for drinking or irrigation purposes. The Piper tri-linear diagram suggests the dominant water type in the study area was the Ca-HCO3 type, where Ca and HCO3− are the principal cations and anions, respectively. A bivariate analysis of different hydro-chemical parameters revealed that silicate weathering controls the hydrogeochemical processes in groundwater. Principal component and hierarchical cluster analysis indicate As in groundwater are geogenic in origin under reductive dissolution processes. The moderate correlation between As, Fe, and Mn indicate reductive dissolution of FeOOH and MnOOH plays a vital role in releasing As from sediment to groundwater. Probable cancer risk assessment for both adults and children revealed a higher value than the recommended value of 10−6 according to United Nations Environmental Protection Agency (USEPA), suggesting that people in the area of interest were at high carcinogenic risk.

MPA-RNN: A Novel Attention-Based Recurrent Neural Networks for Total Nitrogen Prediction

Accurately predicting the short- and long-term variations of total nitrogen (TN) is vital for operating the wastewater treatment plants (WWTPs), considering the critical role TN plays in reflecting the eutrophication of wastewater. However, only a few relevant water quality parameters with limited samples can be obtained in WWTPs, which tremendously increases the difficulty in precisely predicting TN concentration. In this study, a multiphase attention-based recurrent neural network (MPA-RNN) is proposed. Benefited from its unique decomposition-summary attention structure, MPA-RNN first learns the temporal correlations and effectively excavates the useful information hidden in the historical data. Then, by designing a two-channel structure to transmit attention information, summary attention can integrate the decomposed information and learn the spatial relationships without information loss. Experimental results demonstrate that MPA-RNN achieves the best performance on both the SML2010 and practical TN datasets with the smallest root-mean-squared error, mean absolute error, and mean absolute percentage error when compared with the other state-of-the-art methods.

Development and Application of a Hydrogeochemical Model for the Groundwater Treatment Process in Waterworks

Drinking water quality is one of the most important factors affecting human health. The task of the waterworks is to purify raw water into drinking water. The quality of drinking water depends on two major factors: the raw water quality, and the treatment measures that are applied in the waterworks. Since the raw water quality develops over time, it must be determined whether the treatment measures currently used are also suitable when the raw water quality changes. For this reason, a hydrogeochemical model relevant to the drinking water quality during the treatment process was developed. By comparing the modeled results with the measured values, with the exception of chloride and sodium, all other relevant water quality parameters were consistent with one another. Therefore, the model proved to be plausible. This was also supported by the results of mass balance. The model can be used to forecast the development of drinking water quality, and can be applied as a tool to optimize the treatment measures if the raw water conditions change in the future.

Determination of cost-effective optimum coagulant dosage for removal of disinfection by-product precursors in water treatment based on the theory of elasticity

Determination of coagulant dosage in drinking water treatment is related to the requirements for drinking water quality as well as the treatment costs. Selection of appropriate coagulant dosages has been an issue for water treatment utilities, though empirical approaches were normally considered or employed. Inspired by the theory of elasticity in microeconomics, this study explored a novel approach for the cost-effective optimum coagulant dosage. This could enable water utilities to achieve the maximum possible removal efficiency of precursors for disinfection byproducts (DBPs) while maintain an economical dosage without incurring an excessive cost. The relationships between DBP formation potential (DBPFP) and several relevant water quality parameters were first examined and evaluated. UV254 was found the most appropriate DBPFP indicator with the highest correlation coefficients. Based on the relationship of UV254 and DBPFP, an approach for determination of cost-effective optimum coagulant dosage was delineated. The results showed that use of the cost-effective optimum coagulant dosage, which account for approximately 33% of optimum coagulant dosage, could achieve 79% of maximum removal efficiencies of UV254 for the source waters tested, thereby substantially reducing the formation of DBPs. Further increase the coagulant dosage was believed uneconomical since the increase in UV254 removal was limited. Similar results were obtained with different coagulants and with raw water samples with diverse water qualities. The results suggest that the proposed approach could provide a mathematical tool for cost-effective optimum coagulant dosage control which could at the same time achieve sufficient removal of natural organic matter to reduce DBPs formation.

A global perspective on assessing groundwater quality

An assessment of global groundwater quality is needed in response to the threats posed by anthropogenic and geogenic contaminants. This essay summarises the challenges involved, including a large number of potentially relevant water quality parameters, the poor availability of data in many regions and the complex nature of groundwater systems. Direct monitoring data can sometimes be augmented by indirect methods such as earth observations, and by involving citizen science. A new web portal is being developed to complement existing databases.

Spatial Persistence of Water Chemistry Patterns Across Flow Conditions in a Mesoscale Agricultural Catchment

AbstractProtecting water quality at catchment scales is complicated by the high spatiotemporal variability in water chemistry. Consequently, determining pollutant sources requires costly monitoring strategies to diagnose causes and guide management solutions. However, recent studies have shown that spatial patterns in water chemistry can be persistent at catchment scales, potentially allowing identification of pollution sources and sinks with just a few sampling campaigns. Here, we tested a new method to quantify spatial persistence (SP) of water chemistry patterns with data from synoptic samplings in 22 headwater subcatchments within a 375 km2 catchment in western France (March 2018 to July 2019). This new method to quantify SP reduces dependence on long‐term metrics such as flow‐weighted concentrations, which are usually uncertain or unavailable. We applied the method to 16 ecologically relevant water quality parameters, including soluble reactive phosphorus, nitrate, and dissolved organic carbon. The results showed an average SP of 0.68 among parameters during the study period. For most parameters, SP was higher during the high‐flow winter period but lower and more variable during the low‐flow summer period. We found that the SP ultimately depended on the ratio between the temporal and spatial coefficients of variation (variance explained: 70%) rather than the temporal synchrony among subcatchments (variance explained: 4%). These results demonstrate that in these temperate catchments, synoptic sampling during the high‐flow winter period allows efficient identification of source and sink subcatchments, while more frequent samplings are needed to characterize ecological conditions at low flow.

Regional leachate discharge, monitoring and the associated riverine pollutants propagation model simulation of Sungai Sarawak in Malaysia

The Sarawak River also known as Sungai Sarawak serves as a vital water source for the residents in Kuching City and surrounding popular areas. Like many urban rivers elsewhere, Sungai Sarawak and its main tributaries are exposed to the potential pollution caused by leachate discharge and other pollutants. In order to preserve the cleaner water production, mundane sustainable water source as well as provide green environmental spots for tourist attraction, the water quality of the river needs to be continuously monitored to avoid or minimize potential unwanted water source contamination. The present work aims primarily to conduct a parametric study to predict the impact of leachate and other pollutants towards the water quality of Sungai Sarawak and its main tributaries. Relevant water quality parameters were selected as the indicators to assess the impacts of leachate discharges and other relevant pollutants by employing QUAL2K modelling system. The environmental parameters include DO, BOD, NH3-N, and total suspended solids (TSS) were evaluated. The simulation results illustrated the leachate discharge and other pollutants would not significantly deteriorate the water quality of Sungai Sarawak during normal operations (baseline situation). In the event of unwanted leakages, untreated and sudden release of leachate at Sungai Sarawak Kiri in normal riverine flow (Scenario #1) and low riverine flow (Scenario #2) would result in serious contamination of these rivers. High deterioration of Sungai Sarawak water quality also can be seen in Scenario #3 where the unwanted leakages or untreated and sudden release of leachate at the river mainstem with a low riverine flow which the concentrations of water quality parameters would degrade to Class III-V. The model also shows that three parameters that highly contributed to the deterioration of the baseline water quality based on Scenario #1, #2 and #3 which are BOD, NH3-N, and TSS. The BOD concentration increases by 270% in Scenario #1, 370% in Scenario #2 and 510% in Scenario #3. The NH3-N concentration increases by 390% in Scenario #1, 456% in Scenario #2 and 583% in Scenario #3. The TSS concentration also increases by 275% in Scenario #1, 367% increase in Scenario #2 and 385% in Scenario #3. This study recommends continuous monitoring, proper planning and, control of human activities to ensure that developments within the watershed do not contribute to the degradation of Sungai Sarawak water quality. The study also makes comparisons with other rivers elsewhere and comes up with recommendations in the effort to have more practical and implementable measures as a safety framework for Sungai Sarawak and its tributaries. Lastly, suitable advanced treatment systems such as industrial-scale hybrid membrane-microbial fuel cell systems are recommended for slow-to medium flow rate leachate-riverine treatment applications.

Relative developmental toxicities of reclaimed water to zebrafish embryos and the relationship with relevant water quality parameters

Reclaimed water recharging rivers is an important way to solve the problem of water shortage. However, reclaimed water contains some toxic contaminants, which will cause ecological and health risks. The objective of this study is to explore the relationship between developmental toxicities and relevant water quality parameters. Zebrafish embryos were exposed to secondary effluent, wastewater with advanced treatment (Tertiary treatment effluent) and blank (Aerated tap water). The samples taken in April showed higher biological toxicity to embryos, as the maximum value of mortality and malformation reached to 47.5 % for secondary effluent, 75 % for wastewater with advance treatment, while the blank was just 2 % at 120 hours post fertilization. The tested samples also showed significantly adverse effect on hatchability of zebrafish. The hatching rates of embryos exposed to secondary effluent and tertiary treatment effluent were much lower than blank. And significant delay in hatching time existed during the hatching period. The advanced treatment did not show beneficial effects for reducing acute toxicity. The main factor resulted in hatching inhibition may be ammonia especially the free ammonia, as it showed highest coefficient with hatching rate. The no observed effect concentration (NOEC) of ammonia for mortality and malformation were 5 ​mg/L and 10 ​mg/L respectively. The lowest observed effect concentration (LOEC) of ammonia for body length and hatchability were both 2 ​mg/L, while the concentration of free ammonia was 0.19 ​mg/L. Considering the biological toxicity of ammonia on aquatic organism, the discharge concentration of ammonia is advised to be controlled below 2 ​mg/L.

Spatial and temporal variations in river water quality of the Middle Ganga Basin using unsupervised machine learning techniques.

In this study, cluster analysis (CA), principal component analysis (PCA) and correlation were applied to access the river water quality status and to understand spatiotemporal patterns in the Ganga River Basin, Uttara Pradesh. The study was carried out using data collected over 12years (2005-2017) regarding 20 water quality parameters (WQPs) covering spatially from upstream to downstream Ankinghat to Chopan, respectively (20 stations under CWC Middle Ganga Basin). The temporal variations of river water quality were established using the Spearman non-parametric correlation coefficient test (Spearman R). The highest Spearman R (-0.866) was observed for temperature with the season and a very significant p value of (0.0000). The parameters EC, pH, TDS, T, Ca, Cl, HCO3, Mg, NO2 + NO3, SiO2 and DO had a significant correlation with the season (p < 0. 05). K-means clustering algorithm grouped the stations into four different clusters in dry and wet seasons. Based on these clusters, box and whisker plots were generated to study individual clusters in different seasons. The spatial patterns of river WQ on both seasons were examined. PCA was applied to screen out the most significant water quality parameters due to spatial and seasonal variations out of a large data set. It is a data reduction process and a more conventional way of speeding up any machine learning algorithms. A reduced number of three principal components (PCs) were drawn for 20 WQPs with an explained total variance of 75.84% and 80.57% is observed in the dry and wet season, respectively. The parameters DO, EC_ Gen, P-Tot, SO4 are the most dominating parameters with PC score more than 0.8 in the dry season; similarly, TDS, K, COD, Cl, Na, SiO2 in the wet season. The different components of water quality monitoring, such as spatiotemporal patterns, scrutinize the most relevant water quality parameters and monitoring stations are well addressed in this study and could be used for the better management of the Ganga River Basin.

Analysis of the regional spectral properties in northwestern South China Sea based on an empirical orthogonal function

This study presents an analysis of the spectral characteristics of remote sensing reflectance (Rrs) in northwestern South China Sea based on the in situ optical and water quality data for August 2 018. Rrs was initially divided into four classes, classes A to D, using the max-classification algorithm, and the spectral properties of whole Rrs were characterized using the empirical orthogonal function (EOF) analysis. Subsequently, the dominant factors in each EOF mode were determined.The results indicated that more than 95% of the variances of Rrs are partly driven by the back-scattering characteristics of the suspended matter. The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient. Furthermore, the first EOF modes of the four classes of Rrs (A-D Rrs-EOF1) significantly contributed to the total variances of each Rrs class. In addition, the correlation coefficients between the amplitude factors of class A-D Rrs-EOF1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones. The spectral shape of class A Rrs-EOF1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter (CDOM). The spectral shape of class B Rrs-EOF1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM (ag (λ)), whereas the spectral shape of class C Rrs-EOF1 was governed by the back-scattering characteristics but not affected by the suspended matter. The spectral shape of class D Rrs-EOF1 exhibited a relatively good correlation with all the water quality parameters, which played a significant role in deciding its spectral shape.

Field Experience of Fluoride Nilogon:A Method of Fluoride Removal from Groundwater

Field trial of a patented fluoride removal method, based on precipitation–adsorption, has been carried out in some villages of Assam, North East India, with groundwater sources containing 1.8–20 mg/l initial [F – ] at small community (220 l) and household (15 l) levels. Pre-acidified water containing 0.68 mM phos-phoric acid was treated in a crushed limestone bed (1–20 mm) for 3 h and filtered through a sand–gravel filter to retain a desired 0.7 mg/l [F – ] with pH of 7.44–7.9 and relevant water quality parameters meeting WHO guidelines. A slightly higher dose can totally remove fluoride. The fluoride removal has been found to be independent of initial [F – ]. The units have been showing consistent results till now for over five and half years and 4625 batches of use without requiring any interventions like reactivation, replacement or re-plenishment of the limestone bed. With consistent re-moval of fluoride from any initial concentration to a desired concentration, a recurring cost of only Rs 0.005/l of water and an estimated life of the lime-stone bed of about 50 years or 39,000 batches, this safe, environment-friendly and simple method without requiring electricity, has been gaining popularity as Fluoride Nilogon.

Using multivariate techniques as a strategy to guide optimization projects for the surface water quality network monitoring in the Velhas river basin, Brazil.

Surface water quality monitoring networks are usually deployed and rarely re-evaluated with regard to their effectiveness. In this sense, this work sought to evaluate and to guide optimization projects for the water quality monitoring network of the Velhas river basin, using multivariate statistical methods. The cluster, principal components, and factorial analyses, associated with non-parametric tests and the analysis of violation to the standards set recommended by legislation, identified the most relevant water quality parameters and monitoring sites, and evaluated the sampling frequency. Thermotolerant coliforms, total arsenic, and total phosphorus were considered the most relevant parameters for characterization of water quality in the river basin. The monitoring sites BV156, BV141, BV142, BV150, BV137, and BV153 were considered priorities for maintenance of the network. The multivariate statistical analysis showed the importance of a monthly sampling frequency, specifically the parameters considered most important.

Effect of operating conditions and interfering substances on photochemical degradation of a cationic surfactant

ABSTRACTThis work investigates the degradation kinetics of a recalcitrant organic pollutant, cetyltrimethylammonium bromide (CTAB), using direct UV and UV–H2O2 advanced oxidation processes. Direct photolysis at 253.7 nm showed only 55% degradation up to fluence dose of 40.65 J/cm2 for an initial CTAB concentration of 100 mg/L. The apparent fluence-based pseudo-first-order rate constant and quantum yield were 2.29(±0.325) × 10−5 cm2/mJ and 0.305(±0.043) mol/Einstein, respectively. In case of UV–H2O2, >99% degradation was observed up to a fluence dose of 0.79 J/cm2. The rate constant was ∼200 times higher compared to direct photolysis, which was due to hydroxyl radical generation in the UV–H2O2 process. The second-order hydroxyl radical rate constant for CTAB was found to be 1.59(±0.18) × 109 M−1 s−1. The effects of H2O2 dose, initial CTAB concentration and relevant water quality parameters (pH, alkalinity and nitrate concentrations) were studied; all of these influenced the rate constants. CTAB degradation was also examined in the municipal wastewater matrix. It is concluded that UV–H2O2 represents an efficient treatment process for CTAB in environmental matrices.

Algal Bioproductivity in Turbulent Water: An Experimental Study

Excessive growth of biomass causes eutrophication and other related water quality problems. For the past several decades, these problems have been managed based on the principle of limiting nutrient, which is to reduce the loading of essential nutrients—either nitrogen or phosphorus—through point and non-point waste source control. More recent research efforts indicated that eutrophication of a natural water body such as a lake or a reservoir can be controlled alternatively by altering its turbulent intensity. The success of this alternative approach depends on more knowledge on the intimate relationship between turbulent intensity and the bioproductivity of a water body. In this experimental study, an oscillating grid turbulence (OGT) reactor was constructed to evaluate the effect of turbulent pulsation strength in terms of vibration frequency on algae bioproductivity under adequate nutrient, light, and temperature conditions. Experimental results showed that moderate turbulent intensity with vibration frequency of 0.5 Hz or less increased algal growth; with a vibration frequency of 1.0 Hz, the observed peak chlorophyll a (Chl-a) concentration in the reactor was 0.112 mg/L. The experimental results also showed that strong turbulent intensity with vibration frequency of 1.5 Hz or more reduced algal growth; with vibration frequency of 1.5 Hz, the observed peak Chl-a concentration in the reactor was only 0.06 mg/L, which was even lower than the observed peak Chl-a concentration in the reactor with stationary water. In this study, the effect of water turbulence on algal bioproductivity was further verified with experimental data on the variations of other relevant water quality parameters in the OGT reactor including total nitrogen (TN), total phosphorus (TP), pH, and dissolved oxygen (DO).

High chlorophyll a concentration in a low nutrient context: discussions in a subtropical lake dominated by Cyanobacteria

&lt;p&gt;Temporal variability in some water quality parameters can play an important role in determining the presence and abundance of primary producers, and consequently in the trophic state and other characteristics and uses of lake ecosystems. In this sense, the present study aimed at understanding temporal dynamics of some trophic relevant water quality parameters in different time scales and their correlation and influence in phytoplankton biomass (chlorophyll &lt;em&gt;a&lt;/em&gt;) in a shallow subtropical coastal lake. Peri Lake is located in Florianópolis island in Southern Brazil and samples were taken monthly between March 2007 and February 2013. The lake showed low dissolved nutrients concentration, especially phosphorus (P) (median dissolved P: 2.0 µg.l&lt;sup&gt;-1&lt;/sup&gt;) and high chlorophyll &lt;em&gt;a&lt;/em&gt; (median: 20.8 µg.l&lt;sup&gt;-1&lt;/sup&gt;) concentration. Total nitrogen (TN) concentration varied broadly, with a median of 672.8 µg L&lt;sup&gt;-1&lt;/sup&gt;, and total P (TP) concentration was low (median: 13.5 µg L&lt;sup&gt;-1&lt;/sup&gt;). A seasonal pattern of variation concerning dissolved and total P and chlorophyll a concentration was observed, associated mainly with temperature and wind speeds, but no clear pattern was observed for nitrogen (N) fractions. Significant differences were observed in different years for some parameters, with higher chlorophyll a and lower N concentration in the last three years sampled. The lake was considered potentially P limited during the majority of the study period and a positive correlation was found between chlorophyll &lt;em&gt;a&lt;/em&gt; and total and dissolved P concentration. Phytoplankton biomass (as chlorophyll &lt;em&gt;a&lt;/em&gt;) was apparently controlled by water temperature and P availability (TN:TP ratio and dissolved P). Water transparency (as Secchi depth) was strongly and negatively influenced by chlorophyll &lt;em&gt;a&lt;/em&gt; concentration. &lt;em&gt;Cylindrospermopsis raciborskii&lt;/em&gt; abilities to compete for P and light seem to be important factors determining its success and dominance in this low P coastal ecosystem. The fluctuating P supply, probably associated to sediment resuspension by wind in this shallow waterbody, is an advantageous factor for cyanobacteria and has an important role in chlorophyll &lt;em&gt;a&lt;/em&gt; dynamics. Thus, high chlorophyll &lt;em&gt;a&lt;/em&gt; concentration in this subtropical lake seems to be related to the P-limited condition, shallowness and low water column transparency, which are probably favouring the dominance of &lt;em&gt;C. raciborskii&lt;/em&gt;, especially in higher summer temperatures, and leading to high chlorophyll &lt;em&gt;a&lt;/em&gt; concentration even in a low dissolved nutrient environment.&lt;/p&gt;

10-Day survival of Hyalella azteca as a function of water quality parameters

Estuarine systems are among the most impacted ecosystems due to anthropogenic contaminants; however, they present unique challenges to toxicity testing with regard to varying water quality parameters. The euryhaline amphipod species, Hyalella azteca, is widely used in toxicity testing and well suited for testing estuarine water samples. Nevertheless, the influence of relevant water quality parameters on test endpoints must be quantified in order to efficiently use this species for routine monitoring. Here, we studied the influence of five water quality parameters: electrical conductivity, pH, un-ionized ammonia, dissolved oxygen and temperature, on H. azteca survival in a water column toxicity test. A model was developed to quantify and predict the independent and interacting effects of water quality variables on 10-day survival. The model allows simultaneous assessment of multiple potential predictors recorded during the tests. Data used for modeling came from 1089 tests performed on ambient water samples over a period of three years (2006–2008). The final model reflects significant effects of predictors and their two-way interactions. The effect of each level of all predictors on survival probability of H. azteca was examined by comparing levels of each predictor at a time, while holding all others at their lowest (reference) level. This study showed that predictors of survival in water column tests should not be evaluated in isolation in the interpretation of H. azteca water column tests. Our model provides a useful tool to predict expected control survival based on relevant water quality parameters, and thus enables the use of H. azteca tests for toxicity monitoring in estuaries with a wide range of water quality conditions.